The present invention relates to a four wheel drive motor vehicle having a central differential, and more particularly to a control system comprising a fluid operated clutch device for controlling the central differential.
A conventional four-wheel drive motor vehicle has the central differential having a control device for restricting a differential operation and for controlling distribution of a torque to front and rear wheels. Recently, the central differential is used for variably controlling the torque distribution, or used as a reduction gear or speed-up gear, thereby improving driveability, operability, stability and braking effect.
In order to provide the above mentioned multiple functions of the central differential, it is necessary to provide a plurality of friction engagement elements such as a fluid operated multiple-disk friction clutch and a brake on the differential. It is very important how to dispose these elements on the differential.
Japanese Patent Laid-open Application 4-27622 filed by the same applicant discloses a four-wheel drive motor vehicle providing a central differential which comprises a complex planetary gear device and a control device. The control device comprises first and second fluid operated multiple-disk friction clutches and the brake for a 5th speed. The first clutch is provided for transmitting the power of an engine from a transmission to front and rear wheels. The second clutch is provided for restricting the differential operation of the central differential and variably distributing torque to front and rear wheels of the vehicle. The clutches and the brake are independently constructed and disposed side by side along an axis of an output shaft of the transmission. The second clutch is connected to a carrier of the central differential through three connecting parts by welding. Furthermore, an oil chamber of the second clutch is provided in a rotating drum.
Accordingly, the transmission becomes long in the axial direction, resulting in increase of the size and weight thereof. Hence the legroom of the vehicle is reduced. Further, a lubrication system for the differential is complicated.
Since the control device connected to the central differential is complicated in construction, it is very difficult to mount the control device on the central differential.
When a drum of the fluid operated clutch is rotated, pressure of oil in the drum is exerted on a piston mounted in the drum by centrifugal force, so that the control operation for the torque is deteriorated.